The present invention relates to variable capacitance devices and, specifically, to variable capacitance devices based on microelectromechanical systems (MEMS) devices.
Conventional MEMS varactors (also known as capacitive switches or switched capacitors) typically have a very small tuning voltage range, i.e., the voltage range over which the device capacitance may be reliably controlled between the minimum and maximum capacitance in an analog manner.
Binary state MEMS devices such as, for example, interferometric modulators (IMODs), are characterized by two stable states with two different capacitances. Thus, such devices can be used as variable capacitance devices, but have had limited utility in that only two stable capacitance values are typically represented, i.e., one corresponding to the relaxed state of the device (i.e., “up state” capacitance), and one corresponding to the actuated state of the device (i.e., “down state” capacitance).
A variety of attempts have been made to come up with devices that have more of a range of capacitance values with varying degrees of success. However, most such devices require undesirable overhead such as, for example, independent device control signals and circuitry, additional switching circuitry, more than two terminals, etc. Widening and/or stabilizing the tuning range of such devices will make them suitable to a much broader range of applications.